2014 Mercedes-Benz S500 Plug-In Hybrid: Plutocratic 78 MPG Plug-In

The 2014 Mercedes-Benz S500 Plug-In Hybrid may not have a catchy name, but we've been expecting it for some time--ever since the marque showed off its Vision S500 Plug-In Hybrid Concept back in 2009, in fact.

No self-respecting luxury automaker can be without a plug-in model these days. Rival Audi might see diesel as the future of luxury and sport sedans, but Mercedes joins fellow Stuttgart automaker Porsche in offering a plug-in version of its high-end sedan.

Performance is as important as economy, here. On that front, the S500 does well.

The power source is a turbocharged 3.0-liter, V-6 gasoline engine paired in parallel with an electric motor and trunk-mounted lithium-ion battery pack. The engine alone is capable of a hefty 328 horsepower and 354 pounds-feet of torque, while electric assistance adds another 80 kilowatts (107 horsepower) and 250 lb-ft.

Where the Vision S500 concept touted figures of 70 mpg combined and a 0-60 time of around six seconds, the production S500 Plug-In does better on both fronts--78 mpg combined and just 5.5 seconds. The former is measured on the European combined fuel economy cycle, so eventual EPA numbers will be lower. You might have noticed how similar the car's economy and performance figures are to the Porsche Panamera S e-Hybrid--marginally better on combined gas mileage, marginally slower to accelerate.

As usual with plug-in hybrids, we'd add that those figures hinge heavily on the way economy tests are conducted. The S500's 'E-MODE' electric-only setting doles out 18 miles of range (again in European testing), but those 18 miles will contribute heavily to the car's overall efficiency rating, so take '78 mpg' with a pinch of salt.

Of course, some owners may see more on the car's fancy wide-screen TFT display, if they're able to recharge at either end of their commute.

Other driving modes available in the S500 include 'HYBRID'--which is rather self-explanatory--'E-SAVE', which is essentially a battery-hold mode letting you slip into EV-only urban centers, and 'CHARGE', which diverts some of the engine's power toward charging the battery. Leave the 'Intelligent HYBRID' energy management system to its own devices and the S500 will slip seamlessly into whichever mode it feels is appropriate--using the car's satellite navigation system to determine the route ahead and plan accordingly.

That way, the car can make best use of its modest electric range to save gas, knowing where it can gain back some electric miles--for example, if it knows you're approaching a hill in the next few minutes. The drivetrain can also shut the engine off entirely when coasting, saving even more fuel.

The driver is shown all this on the car's huge interior display screens, while haptic feeback from the car's gas pedal allows you to tailor your driving for maximum efficiency.

The 2014 Mercedes-Benz S500 Plug-In Hybrid will debut at this September's Frankfurt Auto Show, with sales expected some time next year.